Hybrid charger and inverter system

ABSTRACT

An AC-AC converter can include a stack of four switches. An input of the converter can be coupled across the stack of four switches, and an output of the converter can be taken from first terminal coupled to a connection point of first and second switches of the stack and a second terminal coupled to a connection point of third and fourth switches of the stack. The converter can further include a controller that operates the switches such that during a positive half cycle of an AC input voltage, the first and second switches are operated with an alternating 50% duty cycle and the third and fourth switches are constantly on, and during the negative half cycle of the AC input voltage, the third and fourth switches are operated with an alternating 50% duty cycle and the first and second switches are constantly on.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.63/261,544, filed Sep. 23, 2021, entitled “Hybrid Charger and InverterSystem”, and U.S. Provisional Application No. 63/261,545, filed Sep. 23,2021, entitled “Hybrid Charger and Inverter System,” and U.S.Provisional Application No. 63/261,548, filed Sep. 23, 2021, entitled“Hybrid Charger and Inverter System,” the disclosures of which areincorporated by reference in their entirety for all purposes.

BACKGROUND

In many applications it may be desirable to provide one or morealternating current (AC) convenience outlets from battery-based directcurrent (DC) power system. These AC convenience outlets may be employedby a user for powering any of a variety of AC loads, ranging from laptoppower supplies to household appliances and the like. Exemplarybattery-based DC power systems may include electric vehicles,grid-battery-storage systems, portable power banks, and other systems.Battery-based DC systems may have an AC grid connection for charging thebattery and an associated charger (i.e., AC-DC converter) for convertingthe AC grid power to DC power suitable for charging the battery. In someapplications, inclusion of an additional converter to generate the ACvoltage needed for the convenience outlet(s) may not be desirable.

SUMMARY

In some cases, it may be desirable to repurpose this converter togenerate the AC voltage needed for the convenience outlet. For example,this can reduce power device component count, cost, and weight of thebattery-based DC power system. Exemplary arrangements along these linesare described herein.

An electrical system can include a first bidirectional AC-DC converterhaving an AC input couplable to an AC grid connection and a DC outputcouplable to a battery, and a second bidirectional AC-DC converterhaving an AC input selectively couplable to the AC grid connection or aconvenience outlet and a DC output couplable to the battery.

The second bidirectional AC-DC converter AC input may be selectivelycouplable to the AC grid connection or the convenience outlet by firstand second switches. The first switch can be coupled between the ACinput of the first bidirectional AC-DC converter and the AC input of thesecond bidirectional AC-DC converter, and the second switch can becoupled between the AC input of the second bidirectional AC-DC converterand the convenience outlet. The second switch can be further coupledbetween the first switch and the convenience outlet. The first andsecond switches can be single pole switches.

The electrical system can further include a controller configured totoggle the first and second switches and control operation of the firstand second bidirectional converters to operate in one of a plurality ofmodes including a two-stage charging mode in which the controlleroperates both the first and second bidirectional converters in a forwarddirection to charge the battery, a single-stage charging mode in whichthe controller operates the first bidirectional converter in a forwarddirection to charge the battery and operates the second bidirectionalconverter in a reverse direction to power the convenience outlet, and anon-charging mode in which the controller idles the first bidirectionalconverter and operates the second bidirectional converter in a reversedirection to power the convenience outlet. In the two-stage chargingmode the controller can close the first switch and open the secondswitch, and in the single-stage charging mode and the non-charging modethe controller can open the first switch and close the second switch.

The electrical system can further include a controller configured tocontrol operation of the first and second bidirectional converters tooperate in one of a plurality of modes including a two-stage chargingmode in which the controller operates both the first and secondbidirectional converters in a forward direction to charge the battery, asingle-stage charging mode in which the controller operates the firstbidirectional converter in a forward direction to charge the battery andoperates the second bidirectional converter in a reverse direction topower the convenience outlet, and a non-charging mode in which thecontroller idles the first bidirectional converter and operates thesecond bidirectional converter in a reverse direction to power theconvenience outlet.

A method performed by a controller of an electrical system having an ACgrid connection, a DC battery connection, an AC convenience outletconnection, two bidirectional AC-DC converters, and a controller caninclude determining whether operation of the convenience outlet isrequired, and, if not, coupling AC inputs of the two bidirectional AC-DCconverters to the AC grid connection and operating the two bidirectionalAC-DC converters in a forward direction to charge a DC battery coupledto the DC battery connection. If operation of the convenience outlet isrequired, the method can further include determining at least one ofwhether an AC grid is connected to the AC grid connection and whetherbattery charging is required, and, if either an AC grid is not connectedor battery charging is not required, idling a first of the twobidirectional AC-DC converters, coupling an AC input of a second of thetwo-bidirectional AC-DC converters to the convenience outlet, andoperating the second bidirectional AC-DC converter in a reversedirection to power the convenience outlet.

If an AC grid is connected and battery charging is required, the methodcan further include determining if the connected AC grid voltage issuitable for the convenience outlet. If the AC grid voltage is suitablefor the convenience outlet the method can further include coupling ACinputs of the two bidirectional AC-DC converters to the AC gridconnection and operating the two bidirectional AC-DC converters in aforward direction to charge a DC battery coupled to the DC batteryconnection and coupling the AC grid to the convenience outlet. If the ACgrid voltage is not suitable for the convenience outlet, the method canfurther include coupling an AC input of a first of the two bidirectionalAC-DC converters to the AC grid connection, operating the firstbidirectional AC-DC converter in a forward direction to charge a DCbattery coupled to the DC battery connection, coupling an AC input of asecond of the two-bidirectional AC-DC converters to the convenienceoutlet, and operating the second bidirectional AC-DC converter in areverse direction to power the convenience outlet.

A method performed by a controller of an electrical system having an ACgrid connection, a DC battery connection, an AC convenience outletconnection, two bidirectional AC-DC converters, a plurality of switches,and a controller, can include determining whether operation of theconvenience outlet is required and, if not, toggling the plurality ofswitches to couple AC inputs of the two bidirectional AC-DC convertersto the AC grid connection and operating the two bidirectional AC-DCconverters in a forward direction to charge a DC battery coupled to theDC battery connection. If operation of the convenience outlet isrequired, the method can further include determining at least one ofwhether an AC grid is connected to the AC grid connection and whetherbattery charging is required, and, if either an AC grid is not connectedor battery charging is not required, idling a first of the twobidirectional AC-DC converters, toggling the plurality of switches tocouple an AC input of a second of the two-bidirectional AC-DC convertersto the convenience outlet, and operating the second bidirectional AC-DCconverter in a reverse direction to power the convenience outlet.

If an AC grid is connected and battery charging is required, the methodcan further include determining if the connected AC grid voltage issuitable for the convenience outlet. If the AC grid voltage is suitablefor the convenience outlet the method can further include toggling theplurality of switches to couple AC inputs of the two bidirectional AC-DCconverters to the AC grid connection and operating the two bidirectionalAC-DC converters in a forward direction to charge a DC battery coupledto the DC battery connection and coupling the AC grid to the convenienceoutlet. If the AC grid voltage is not suitable for the convenienceoutlet, the method can further include toggling the plurality ofswitches to couple an AC input of a first of the two bidirectional AC-DCconverters to the AC grid connection and to couple an AC input of asecond of the two-bidirectional AC-DC converters to the convenienceoutlet, operating the first bidirectional AC-DC converter in a forwarddirection to charge a DC battery coupled to the DC battery connection,and operating the second bidirectional AC-DC converter in a reversedirection to power the convenience outlet.

An electrical system can include an isolated bidirectional converterhaving an input couplable to an AC grid connection and an outputcouplable to a battery and a non-isolated converter having an inputcoupled to the input of the isolated bidirectional converter andselectively couplable to the AC grid connection and an AC output coupledto a convenience outlet. The input of the isolated bidirectionalconverter and the input of the non-isolated converter can be selectivelycouplable to the AC grid connection by a switch. The switch can be asingle pole switch. The electrical system can further include acontroller configured to toggle the switch and control operation of theisolated bidirectional converter and the non-isolated converter tooperate in one of a plurality of modes, including a charging mode inwhich the isolated bidirectional converter operates in a forwarddirection to charge the battery and the non-isolated converter powersthe convenience outlet from the grid connection and a non-charging modein which the isolated bidirectional converter operates in a reversedirection to power the non-isolated converter from the battery and thenon-isolated converter powers the convenience outlet. In the chargingmode the controller can close the switch, and in the discharging modethe controller can open the switch.

The charging mode can include at least one of a power factor correctionmode and a harmonics compensation mode. In the power factor correctionmode the isolated bidirectional converter can be operated to correct thepower factor of a load coupled to the convenience outlet such that thegrid connection sees a unity power factor. In the harmonics compensationmode the isolated bidirectional converter can be operated to compensatefor harmonics introduced by the load coupled to the convenience outlet.The discharging mode can include at least one of: a first dischargingmode in which the isolated bidirectional converter is operated in thereverse direction to produce an output voltage having a magnitudetracking the battery voltage; a second discharging mode in which theisolated bidirectional converter is operated in the reverse direction toproduce an output voltage having a magnitude suitable for theconvenience outlet; and a third discharging mode in which the isolatedbidirectional converter is operated in the reverse direction to producean output voltage having a magnitude corresponding to a voltage of theAC grid. In the first discharging mode the isolated bidirectionalconverter can perform regulation of the output voltage for theconvenience outlet. In the second discharging mode the isolatedbidirectional converter can operate as a pass-through. In the thirddischarging mode the isolated bidirectional converter can operate as afixed ratio converter. In each discharging mode the output voltage canbe an AC or a DC voltage.

The AC-AC converter can include a stack of four switching devices. Aninput of the AC-AC converter can be coupled across the stack of fourswitching devices, and an output of the AC-AC converter can be takenfrom a connection point of first and second switching devices of thestack and a junction of third and fourth switching devices of the stack.The converter can further include input capacitors coupled in seriesacross the input of the AC-AC converter, with a connection point of theinput capacitors coupled to a connection point of the second and thirdswitching devices. The converter can further include at least one outputfilter inductor and at least one output filter capacitor coupled to theoutput of the AC-AC converter. The AC-AC converter can further include aresonant tank made up of at least one resonant capacitor and at leastone resonant inductor, wherein the resonant tank facilitates zerovoltage switching of the switching devices. Alternatively, the AC-ACconverter can include a plurality of bidirectional switching devices,wherein an input of the AC-AC converter is coupled across thebidirectional switching devices and an output of the AC-AC converter istaken from a connection point of the bidirectional switching devices.Such a converter can further include at least one input capacitorcoupled across the input of the AC-AC converter and at least one outputfilter inductor and at least one output filter capacitor coupled to theoutput of the AC-AC converter. The bidirectional switches can beconfigured as a full bridge converter or as a half bridge converter.

A method can be performed by a controller of an electrical system havingan AC grid connection, a DC battery connection, an AC convenience outletconnection, an isolated bidirectional converter, a non-isolatedconverter, and a controller. The method can include determining whetheran AC power source is coupled to the AC grid connection and, if not,operating the isolated bidirectional converter in a reverse direction toprovide power to the non-isolated converter from the battery andoperating the non-isolated converter to power the convenience outlet. Ifan AC power source is coupled to the AC grid connection, the method canfurther include operating the isolated bidirectional converter in aforward direction to charge the battery from the AC grid and operatingthe non-isolated converter to power the convenience outlet from the ACgrid. Operating the isolated bidirectional converter in a forwarddirection to charge the battery from the grid and operating thenon-isolated converter to power the convenience outlet from the AC gridcan further include comprises at least one of a power factor correctionmode and a harmonics compensation mode. In the power factor correctionmode, operating the isolated bidirectional converter can includecorrecting the power factor of a load coupled to the convenience outletsuch that the grid connection sees a unity power factor. In theharmonics compensation mode, operating the isolated bidirectionalconverter can include compensating for harmonics introduced by the loadcoupled to the convenience outlet.

Operating the isolated bidirectional converter in the reverse directionto provide power to the non-isolated converter from the battery andoperating the non-isolated converter to power the convenience outlet caninclude at least one of three discharging modes. In a first dischargingmode, operating the isolated bidirectional converter in the reversedirection can include producing an output voltage having a magnitudetracking the battery voltage. In a second discharging mode, operatingthe isolated bidirectional converter in the reverse direction caninclude producing an AC output voltage having a magnitude suitable forthe convenience outlet. In a third discharging mode, operating theisolated bidirectional converter in the reverse direction can includeproducing an AC output voltage having a magnitude corresponding to avoltage of the AC grid. In the first discharging mode operating thenon-isolated converter can include regulating the output voltage for theconvenience outlet. In the second discharging mode, operating thenon-isolated converter can include operating as a pass-through. In thethird discharging mode, operating the non-isolated converter comprisesoperating as a fixed ratio converter. In each discharging modes theoutput voltage can be an AC or a DC voltage.

An AC-AC converter can include a stack of four switching devices. Aninput of the AC-AC converter can be coupled across the stack of fourswitching devices, and an output of the AC-AC converter can be takenfrom first terminal coupled to a connection point of first and secondswitching devices of the stack and a second terminal coupled to aconnection point of third and fourth switching devices of the stack. TheAC-AC converter can further include first and second series-connectedinput capacitors coupled across the input of the AC-AC converter, with aconnection point of the series-connected input capacitors coupled to aconnection point of the second and third switching devices. The AC-ACconverter can further include at least one output filter inductor and atleast one output filter capacitor coupled to the output of the AC-ACconverter. The at least one filter inductor can include a first filterinductor coupled between the first terminal and a load. The at least onefilter inductor can include a second inductor coupled between the secondterminal and the load.

The AC-AC converter can further include a resonant tank made up of atleast one resonant capacitor and at least one resonant inductor. Theresonant tank can facilitate zero voltage switching of the switchingdevices. The resonant tank can be a series resonant circuit coupledbetween the first terminal and the second terminal. The resonant tankcan be a series resonant circuit coupled in parallel with the at leastone output filter inductor.

The AC-AC converter can further include a controller that operates theswitching devices such that during a positive half cycle of an AC inputvoltage, first and second switching devices of the stack are operatedwith an alternating 50% duty cycle and third and fourth switchingdevices of the stack are constantly on, and during the negative halfcycle of the AC input voltage, the third and fourth switching devices ofthe stack are operated with an alternating 50% duty cycle and the firstand second switching devices of the stack are constantly on. During thepositive half cycle, the duration of the on-times of the first andsecond switching devices determine the magnitude of the AC voltagebetween the first and second terminals. During the negative half cycle,the duration of the on times of the third and fourth switching devicesdetermine the magnitude of the AC voltage between the first and secondterminals.

A method performed by a controller of an AC-AC converter having a stackof four switching devices, wherein an input of the AC-AC converter iscoupled across the stack of four switching devices and an output of theAC-AC converter is taken from first terminal coupled to a connectionpoint of first and second switching devices of the stack and a secondterminal coupled to a connection point of third and fourth switchingdevices of the stack, can include, during a positive half cycle of an ACinput voltage, operating first and second switching devices of the stackwith an alternating 50% duty cycle and turning on and leaving on thirdand fourth switching devices of the stack; and during a negative halfcycle of the AC input voltage, operating the third and fourth switchingdevices of the stack with an alternating 50% duty cycle, and turning onand leaving on the first and second switching devices of the stack.During the positive half cycle, the duration of the on-times of thefirst and second switching devices can determine the magnitude of the ACvoltage between the first and second terminals, and, during the negativehalf cycle, the duration of the on times of the third and fourthswitching devices determine the magnitude of the AC voltage between thefirst and second terminals. The switching devices can be operated withzero voltage switching.

An AC-AC converter can include a plurality of bidirectional switchingdevices. An input of the AC-AC converter can be coupled across thebidirectional switching devices, and an output of the AC-AC converter istaken from a connection point of the bidirectional switching devices.The converter can further include at least one input capacitor coupledacross the input of the AC-AC converter and at least one output filterinductor and at least one output filter capacitor coupled to the outputof the AC-AC converter. The bidirectional switches can be configured asa full bridge converter or as a half bridge converter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of an exemplary battery-based DCpower system.

FIG. 2 illustrates prior art configurations for generating an ACvoltage.

FIG. 3A illustrates a two-stage charger circuit in which one phase maybe reused as an inverter to provide an AC voltage.

FIG. 3B illustrates a flow chart of operating modes of the two-stagecharger circuit of FIG. 3A.

FIG. 3C illustrates alternative switch configurations of the chargercircuit in FIG. 3A.

FIG. 4A illustrates a single-stage charger and non-isolated AC-ACconverter circuit that may be used to provide an AC voltage.

FIG. 4B illustrates alternative switch configurations of the chargercircuit in FIG. 4A.

FIG. 5 illustrates power factor correction operating modes of asingle-stage charger and non-isolated AC-AC converter circuit.

FIG. 6A illustrates certain operating modes of a single-stage chargerand non-isolated AC-AC converter circuit.

FIG. 6B illustrates additional operating modes of a single-stage chargerand non-isolated AC-AC converter circuit.

FIG. 7 illustrates a flow chart of operating modes of a single-stagecharger and non-isolated AC-AC converter circuit.

FIG. 8 illustrates exemplary topologies for a non-isolated AC-ACconverter.

FIG. 9 illustrates further exemplary topologies for a non-isolated AC-ACconverter.

DETAILED DESCRIPTION

In the following description, for purposes of explanation, numerousspecific details are set forth to provide a thorough understanding ofthe disclosed concepts. As part of this description, some of thisdisclosure's drawings represent structures and devices in block diagramform for sake of simplicity. In the interest of clarity, not allfeatures of an actual implementation are described in this disclosure.Moreover, the language used in this disclosure has been selected forreadability and instructional purposes, has not been selected todelineate or circumscribe the disclosed subject matter. Rather theappended claims are intended for such purpose.

Various embodiments of the disclosed concepts are illustrated by way ofexample and not by way of limitation in the accompanying drawings inwhich like references indicate similar elements. For simplicity andclarity of illustration, where appropriate, reference numerals have beenrepeated among the different figures to indicate corresponding oranalogous elements. In addition, numerous specific details are set forthin order to provide a thorough understanding of the implementationsdescribed herein. In other instances, methods, procedures and componentshave not been described in detail so as not to obscure the relatedrelevant function being described. References to “an,” “one,” or“another” embodiment in this disclosure are not necessarily to the sameor different embodiment, and they mean at least one. A given figure maybe used to illustrate the features of more than one embodiment, or morethan one species of the disclosure, and not all elements in the figuremay be required for a given embodiment or species. A reference number,when provided in a given drawing, refers to the same element throughoutthe several drawings, though it may not be repeated in every drawing.The drawings are not to scale unless otherwise indicated, and theproportions of certain parts may be exaggerated to better illustratedetails and features of the present disclosure.

FIG. 1 illustrates a high level block diagram of an arrangement 100including a DC electrical system 101. Electrical system 101 may becoupled to one or more of multiple power sources, including a highvoltage battery 102, a low voltage battery 103, and an AC grid 105. Inthe illustrated example, high voltage battery 102 may have a voltageranging from 400-800V DC, although other voltage ranges may be used ifappropriate for a given application. As used herein, “high voltage”generally means a voltage higher than the nominal utility supply voltagefor plug-in devices in residential or commercial service, e.g., 120V inthe U.S. or 230V in Europe. Similarly, low voltage battery 103 may havea voltage ranging from 30-50V DC, although other voltage ranges may beused if appropriate for a given application. As used herein, “lowvoltage” generally means a voltage lower than the nominal utility supplyvoltage for typical residential or commercial service as describedabove. The charging grid may be any standardized voltage available inthe United States or other regions of the world. In the United States,typical AC grid voltages for residential or commercial service include120V, 208V, and/or 240V AC, including single phase, spilt phase, andthree phase configurations. In various applications, electrical system101 may also be operable to deliver power to one or more of these power“sources,” as well as to its own internal loads (e.g., the tractionmotor(s) of an electric vehicle).

To that end, electrical system 101 may include various power conversioncircuitry, described in greater detail below, for converting electricalenergy received from one or more of the “sources” to a level suitablefor another of the “sources.” For example, electrical system 101 mayinclude circuitry for converting the voltage from AC grid 105 into asuitable voltage for charging high voltage battery 102 and/or lowvoltage battery 103. This arrangement may be included in applicationssuch as electric vehicles, uninterruptible power supplies, grid batterystorage systems, etc. Additionally or alternatively, electrical system101 may include circuitry for converting the voltage from high voltagebattery 102 and/or low voltage battery 103 to the grid voltage. Suchapplications may include UPSs and grid battery storage systems. In manyapplications, including each of the foregoing as well as others, it mayalso be desirable to provide power to an AC “convenience outlet” 104that may be used to power any of a variety of typical AC loads, such aslaptop chargers, small appliances, etc. There could be any number ofreasons that it may be desirable to use some of the above-describedpower conversion circuitry as an inverter (i.e., DC to AC converter)produce the AC voltage for convenience outlet 104. Some such reasonsinclude cost reduction, weight reduction, size reduction, and the like.

FIG. 2 illustrates two prior art approaches for powering AC convenienceoutlets from battery-based DC power systems. Approach 210 employs anisolated AC-DC charger 216 to convert voltage from the AC grid 215 to alevel suitable for high voltage battery 212. Because of the high batteryvoltage, an isolated inverter 217 is provided to generate the lowvoltage AC (e.g., 120V AC) that powers convenience outlet 226. Approach220 employs an isolated AC-DC charger 226 to convert voltage from the ACgrid 225 to a level suitable for high voltage battery 222. However,because convenience outlet is powered from low voltage battery 223, anon-isolated inverter 227 may be used. (Not shown in approach 220 is amechanism for charging low voltage battery, which may be done from thehigh voltage DC bus corresponding to high voltage. battery 222 and/orfrom the AC bus corresponding to AC grid 225.) A disadvantage of eitherarrangement is the requirement of additional converter hardware, i.e.,isolated inverter 217 or non-isolated inverter 227, which adds cost,complexity, weight, and volume to a given device. Further disadvantagesof approach 220 include the requirement for two conversion stages (aDC-DC boost stage to increase the voltage from the low voltage batteryand an inverter stage to generate the AC voltage) and the potential forhigh current draw from the low voltage battery (depending on the load onthe convenience outlet).

FIG. 3A illustrates a battery based electrical system 300 using a highvoltage battery 302. Electrical system 300 includes dual isolated AC-DCcharger stages 306 and 307. Charger stages 306 and 307 may bebidirectional chargers, allowing for power delivery in either direction,i.e., either as AC-DC converters in the forward direction or DC-ACconverters in the reverse direction. Various examples of such convertersare known to those ordinarily skilled in the art, and thus the detailsof their construction, control, and operation are omitted for brevity.Charger stages 306 and 307 may be operated in parallel in the forwarddirection to charge high voltage battery 302 from AC grid 305, allowingfor the combined power rating of the two stages to be delivered to thebattery for more rapid charging. Additionally, charger stage 307 may beoperated in the reverse direction as an isolated DC-AC converter (i.e.,inverter) allowing for convenience outlet 304 to be powered from highvoltage battery 305. Switches S1 and S2 may be provided to allow fordirectly powering convenience outlet 304 from AC grid 305 if connectedto a suitable voltage and/or for isolating the AC side of charger stage307 from the AC grid when used as an inverter to power convenienceoutlet 304. This can result in various operating modes 310, 320, and330, illustrated on the right side of FIG. 3A.

Operating mode 310 corresponds to the dual stage charging operationdescribed above. In this mode, isolated charger 306 is operated in theforward direction 318 to deliver power from AC grid 305 to high voltagebattery 302. Switch S1 is closed, and switch S2 is opened. Thus, poweris not provided to convenience outlet 304, but the AC side of isolatedcharger 307 is connected to AC grid 305. Isolated charger 307 is alsooperated in the forward direction 319 to deliver power from AC grid 305to high voltage battery 302. In this mode, the amount of power deliveredto high voltage battery 302 is increased, e.g., doubled as compared tomode 320, but convenience outlet may not be available. (In someapplications, if a suitable voltage is supplied by grid 305, switch S2could also be closed, coupling AC grid 305 to convenience outlet 305.Additional overcurrent protection (not shown) for convenience outlet 304may be necessary in this configuration.

Operating mode 320 corresponds to one stage charging, one stageinverting operation as described above. In this mode, isolated charger306 is operated in the forward direction 328 to deliver power from ACgrid 305 to high voltage battery 302. Switch S1 is open, and switch S2is closed. Thus, power from AC grid 305 is not provided to the AC sideof isolated converter 307, which may now be operated in reversedirection 329 as an inverter to power convenience outlet 304. In thismode, the amount of power delivered to high voltage battery 302 isdecreased, e.g., halved as compared to mode 310, but convenience outletis available for use.

Operating mode 330 corresponds to no charging, with one stage invertingoperation. In this mode, isolated charger 306 is not operated, e.g.,because grid 305 is not available. (Mode 330 could also be used when ACgrid 305 is available but high voltage battery 302 is fully charged.Switch S1 is open, and switch S2 is closed. Thus, the AC sides ofconverters 306 and 307 are decoupled/disconnected. Converter 307 may beoperated in reverse direction 329 as an isolated inverter to powerconvenience outlet 304. In the foregoing description, of operating modes310, 320, and 330, switches S1 and S2 are illustrated as single poleswitches; however, double pole switches could be provided to disconnectthe line and/or neutral legs if desired in a given application. Suchconfigurations are illustrated in FIG. 3C in which additional switchpoles S1′ and S2′ are illustrated with switch poles S1 and S1′ havingthe same switching state and switches S2 and S2′ having the sameswitching state.

FIG. 3B illustrates a flow chart of an operating method 380 of theconverter and operating modes of FIG. 3A. The flow chart may beimplemented by any suitable controller circuitry, including aprogrammable controller (such as a microcontroller or microprocessor), afield programmable gate array, discrete logic control circuits,application specific integrated circuits, etc. Beginning at block 381,the controller can determine whether the convenience outlet is required.If not, in block 382, the electrical system can be placed in Mode 1(discussed above) including two stage charging. In this mode, switch S1is closed and switch S2 is open, and both isolated charger stages areoperated in the forward direction to charge the high voltage batteryfrom the AC grid.

In block 381, if the controller determines that the convenience outletis required, then the controller can determine whether the AC grid isavailable and if charging the high voltage battery is required (block383). If either the AC grid is not available or if HV charging is notrequired, the controller can enter Mode 3 (block 384) in which oneconverter is idled and one stage is operated as an inverter. In thismode, switch S1 is open and switch S2 is closed. Otherwise, in block383, if the controller determines that the AC grid is available and HVcharging is required, then in block 385 the controller can determinewhether the grid voltage is suitable for direct connection to theconvenience outlet. If so, the controller can enter mode 4 (block 387)in which one stage is charging, one stage is operating as an inverter,and both switches S1 and S2 are closed. Otherwise, the controller canenter mode 2 (block 386) in which one stage is charging one stage isoperating as an inverter, and switch S1 is open and switch S2 is closed.

FIG. 4A illustrates a battery based electrical system 400 using a highvoltage battery 402. Electrical system 400 includes a single isolatedAC-DC charger stage 406. Charger stage 406 may be a bidirectionalcharger, allowing for power delivery in either direction, i.e., eitheras an AC-DC converter in the forward direction or DC-AC converter in thereverse direction. In some embodiments, isolated charger stage 406 mayalso be operated as a DC-DC converter, as described in greater detailbelow. Additionally, a non-isolated AC-AC converter 407 may be provided,which can convert the voltage appearing at the AC side of converter 406to a suitable level for convenience outlet 404. In some embodiments,non-isolated converter 407 can be operated as a DC-AC converter (i.e.,inverter), as described in greater detail below. Various examples ofboth converter types are known to those ordinarily skilled in the art,and thus the details of their construction, control, and operation areomitted here for brevity, although exemplary AC-AC converters aredescribed below with reference to FIGS. 8 and 9 . Charger stage 406 maybe operated in the forward direction to charge high voltage battery 402from AC grid 405 and also powering AC-AC converter 407, which, in turn,powers convenience outlet 404. Alternatively, charger stage 406 may beoperated in the reverse direction as an isolated DC-AC converter (i.e.,inverter) allowing for convenience outlet 404 to be powered from highvoltage battery 405. Switch S may be provided for isolating the AC sideof charger stage 307 from the AC grid when used as an inverter to powerconvenience outlet 304. This can result in charging operating mode 410and non-charging operating mode 420 illustrated in the lower portion ofFIG. 4A.

Operating mode 410 corresponds to the charging operation describedabove. In this mode, isolated charger 406 is operated in the forwarddirection 418 to deliver power from AC grid 405 to high voltage battery402. Switch S is closed. Thus, power 429 is provided to convenienceoutlet 304 via AC-AC converter 407. Operating mode 420 corresponds tothe not charging operation described above. In this mode, isolatedcharger 406 is operated in the reverse direction 428 to deliver powerfrom high voltage battery 402 to AC-AC converter 407. Switch S is open,thereby isolating the AC grid 405 connection from converters 406 and407. In some embodiments, switch S could be a two pole switch withadditional switch pole S′ serving to disconnect the grid neutralconnection as illustrated in FIG. 4B. In such configurations, switchpoles S and S′ have the same switching state.

Charging mode 410 of electrical system 400 can allow for different HVbattery charging modes to address power factor and harmonics, which areillustrated in FIG. 5 . In a first power factor/harmonics correctedcharging mode 530, a load imposed on convenience outlet 404 may exhibita leading power factor, as illustrated in current/voltage plot 534. Sucha load may also include relatively high harmonic content, which is notshown. As a result, the input side of AC-AC converter 407 may alsoexhibit a leading power factor, as illustrated in current voltage plot537 (and also high harmonic distortion, not shown). To compensate forthis, isolated AC-DC converter 506, operating in the charging mode, maybe operated to exhibit a lagging power factor, as illustrated incurrent/voltage plot 536. More specifically, switching devices of DC-ACconverter 406 may be adjusted so that a phase relationship between theinput current and voltage of converter 406 (as shown in plot 536)corresponds to but is opposite in sense (lagging vs. leading) from aphase relationship between the input current and voltage of converter407 (as shown in plot 537). Additionally, the switching devices ofconverter 406 may be operated to compensate for the harmonic content. Asa result, AC grid 405 sees unity power factor operation, i.e., the inputcurrent and voltage are in phase, and a relatively harmonic free load.In this power factor and/or harmonic corrected mode, the power andreactive power needed to mitigate the harmonics and power factor aresourced from battery 402, which may result in some voltage variation ofthe high voltage battery, as illustrated by high voltage battery plot532 (which also illustrates the overall charging operation). In somecases, convenience outlet 405 may exhibit a lagging power factor, inwhich case converter 406 could be operated to exhibit a leading powerfactor, thereby providing unity power factor operation as seen by grid405.

In a second power factor/harmonics un-corrected charging mode 540, aload imposed on convenience outlet 404 may exhibit a leading powerfactor, as illustrated in current/voltage plot 544. Such a load may alsoinclude relatively high harmonic content, which is not shown. As aresult, the input side of AC-AC converter 407 may also exhibit a leadingpower factor, as illustrated in current voltage plot 547 (and also highharmonic distortion, not shown). However, instead of compensating forthis, isolated AC-DC converter 506, operating in the charging mode, maybe operated to exhibit a unity power factor, as illustrated incurrent/voltage plot 546. As a result, AC grid 405 will not see unitypower factor operation, i.e., the input current and voltage will be outof in phase, and will see the harmonic distortion associated with theload on convenience outlet for. An advantage of un-corrected mode 540 isthat fewer voltage and current measurements are required and the controlof AC-DC converter 406 may be simplified, as it need not adapt to theload presented via convenience outlet 404. The correspondingdisadvantage is that the non-unity power factor and/or harmonicdistortion introduced by the load on convenience outlet 404 will be seenby AC grid 405. Also, while it is in principle possible to separatepower factor correction from harmonic compensation, the additionalsensor and control capabilities required for either are essentially thesame as required for both. Thus, as a practical matter, power factorcorrection and harmonic compensation are likely to be provided together(as in mode 530) or not provided (as in mode 540).

Discharging mode 420 of Electrical system 400 can also allow fordifferent HV battery discharging modes to enhance overall systemefficiency. These different discharging modes 650, 660, and 670 areillustrated in FIG. 6A. In each of the discharging modes, energy flowsfrom high voltage battery 402 to charger/converter 406 via path 602.Converter 406 converts this into an AC voltage delivered to AC-ACconverter 407 via path 606. AC-AC converter 407 then converts this to avoltage suitable for convenience outlet 404, which is delivered via path607.

In a first discharging mode 650, converter 406 may be operated at itsmaximum possible efficiency, meaning it will generate an AC outputvoltage with a magnitude that tracks the battery voltage 652 asillustrated in plot 657. In other words, the magnitude of this voltagewill decrease as the battery discharges. In this mode, AC-AC converter407 will perform the regulation necessary to produce the desired voltage654 (e.g., 120V AC) for convenience outlet 404. As a result, converter407 may exhibit relatively lower efficiency.

In second discharging mode 660, converter 406 may be operated togenerate an AC output voltage suitable for convenience outlet 404, asillustrated in plot 667 (and 664), regardless of battery voltage 662. Asa result, converter 406 may operate with relatively lower efficiency.However, in this mode, AC-AC converter 407 need not perform any furtherregulation, and, as a result, may exhibit very high efficiency.

In a third discharging mode 670, converter 406 may be operated togenerate an AC output voltage 677 corresponding to the normally suppliedgrid voltage (e.g., 240V or 208V AC), without regard to battery voltage672. As a result, converter 406 will operate with an intermediateefficiency between the two previously discussed modes 650 and 660. Inmode 670, AC-AC converter 407 will perform a step-down as in one of thecharging modes discussed above with reference to FIG. 5 , and, as aresult, converter 407 will exhibit an intermediate efficiency betweenthe two previously discussed modes 650 and 660.

Depending on the specifics of a particular implementation, one of theforegoing modes 650, 660, or 670 may be more efficient. Thus, the modeproviding optimal efficiency may be selected.

A second set of discharging modes may also be available for at leastsome topologies of converters 406 and 407, illustrated in FIG. 6B. Inthese discharging mode, isolated bidirectional converter 406 a may beoperated as a DC-DC converter to generate a DC output voltage that maybe passed via path 606 to non-isolated converter 407 a, which may beoperated as an inverter to generate the AC voltage required byconvenience outlet 404. For some converter topologies this may providean overall system efficiency greater than any of the DC-AC modes 650,660, 670 discussed above. In discharging mode 651, converter 406 a maybe operated at its maximum possible efficiency, meaning it will generatean output voltage with a magnitude that tracks the battery voltage 652as illustrated in plot 657 a. In other words, the magnitude of thisvoltage will decrease as the battery discharges. In this mode, DC-ACconverter 407 a will perform the regulation necessary to produce thedesired voltage 654 (e.g., 120V AC) for convenience outlet 404. As aresult, converter 407 a may exhibit relatively lower efficiency.

In discharging mode 661, converter 406 a may be operated to generate anoutput voltage with a magnitude suitable for convenience outlet 404, asillustrated in plot 667 a (and 664), regardless of battery voltage 662.As a result, converter 406 a may operate with relatively lowerefficiency. However, in this mode, DC-AC converter 407 a need notperform any further regulation, instead being used in, for example, anopen loop 1;1 inverter mode. As a result, converter 407 a may exhibitvery high efficiency.

In discharging mode 671, converter 406 a may be operated to generate anoutput voltage 677 a corresponding to the normally supplied grid voltage(e.g., 240V or 208V AC), without regard to battery voltage 672. As aresult, converter 406 a will operate with an intermediate efficiencybetween the two previously discussed modes 650 and 660. In mode 671,DC-AC converter 407 a will perform a step-down as in one of the chargingmodes discussed above with reference to FIG. 5 . For example, converter407 a can operate in an open loop 2:1 step down inverter mode. Asresult, converter 407 a will exhibit an intermediate efficiency betweenthe two previously discussed modes 651 and 661. Depending on thespecifics of a particular implementation, one of the foregoing modes650, 660, or 670 may be more efficient. Thus, the mode providing optimalefficiency may be selected.

FIG. 7 illustrates a flow chart of an operating method 780 of theconverter and operating modes of FIGS. 4-6 . The flow chart may beimplemented by any suitable controller circuitry, including aprogrammable controller (such as a microcontroller or microprocessor), afield programmable gate array, discrete logic control circuits,application specific integrated circuits, etc. Beginning at block 781,the controller can determine whether the AC grid is connected. If not,in block 782, the electrical system can be placed in the dischargingmode 410, which can be selected from discharging modes 650, 660, 670, orthe DC mode discussed above with reference to FIG. 6A. In this mode,switch S is open and isolated converter/charger 406 operates to providepower to converter 407 (and thus convenience outlet 404).

In block 381, if the controller determines that the AC grid isconnected, then the controller can enter charging mode 420 (block 783),which can be selected from power factor correction and harmonicscompensation charging modes 530 or 540 discussed above with reference toFIG. 5 . In this mode, switch S is closed and isolated converter/charger406 operates to provide power to the high voltage battery while the gridpowers converter 407 (and thus convenience outlet 404).

FIG. 8 illustrates exemplary AC-AC converter topologies 891,892, and 893that may be used for converter 407 in the arrangements of FIGS. 4-7 .Each converter topology 891-893 includes a stacked switching arrangementmade up of switches SaP, SaN, SbN, and SbQ. An input AC voltage 856 maybe input across the full switch stack at terminals P and Q. (In the DCembodiment discussed above, this input voltage may also be a DC inputvoltage.) An output AC voltage may be taken from the intermediate nodesa (located at the connection point of switches SaP and SaN) and b(located at the connection point of switches SbN and SbQ). In theillustrated embodiments, switches SaP and SaN are illustrated asn-channel MOSFETs, and switches SbQ and SbN are illustrated as p-channelMOSFETs; however, any suitable switching devices could be used asappropriate for a given implementation. Input capacitors may be coupledacross the input, with their junction point being coupled to the neutralleg switches SaN and SbN. in each of the topologies 891,892, and 893,output terminals a and b may be coupled to convenience outlet 804 bydifferent inductor/capacitor networks further described below.

For operation as an AC-AC converter, each topology 891-893 may beoperated using pulse width modulation to generate the desired outputvoltage for convenience outlet 804. During the positive half cycle of ACinput voltage 856, switches SaP and SaN may be operated with analternating 50% duty cycle, while switches SbN/SbQ are constantly on.The width of the on-time pulses (i.e., the duration of the on times) ofswitches SaP and SaN will determine the magnitude of the AC voltagebetween terminals a and b (and thus presented to convenience outlet804). During the negative half cycle of AC input voltage 856, switchesSbQ and SbN may be operated with an alternating 50% duty cycle, whileswitches SaP/SaN are constantly on. The width of the on-time pulses(i.e., the duration of the on times) of switches SbQ and SbN willdetermine the magnitude of the AC voltage between terminals b and a (andthus presented to convenience outlet 804). This PWM mode of operation isapplicable to all of the operating modes described above with referenceto FIGS. 4-7 in which converter 407 provides AC voltage regulation forconvenience outlet 404/804. Alternatively, converter topologies may alsooperate in a pass-through mode, in which the input voltage appearingacross terminals P/Q is passed directly to output terminals a/b. In thismode, switches SaP an SaQ are turned on and switches SbQ and SbN areturned off. This passthrough mode of operation is applicable to all ofthe operating modes described above with reference to FIGS. 4-7 in whichconverter 407 does not provide AC voltage regulation for convenienceoutlet 404/804.

In topology 891, output filter inductors Lo and output filter capacitorCo are provided to smooth the output voltage delivered to convenienceoutlet 804. In topologies 892 and 893, resonant capacitor Cr andresonant inductor Lr may also be provided to form a resonant tank thatallows for zero voltage switching (ZVS) of the switching devices. Morespecifically, when alternating from the positive half cycle to thenegative half cycle, or vice versa, resonance of the tank circuitprovides a current reversal to force the filter inductor currentnegative allowing for zero voltage switching.

FIG. 9 illustrates additional AC-AC topology configurations thatincorporate bidirectional switches. Topology 894 illustrates a fullbridge AC-AC converter using bidirectional switches SaP, SbP, SaN, andSbN. Topology 895 illustrates a half bridge AC-AC converter withswitches SaP and SaN. In each configuration, an input AC voltage 856 maybe input at terminals P and Q. In the full bridge configuration 894, anoutput AC voltage may be taken from the intermediate nodes a (located atthe connection point of switches SaP and SaN) and b (located at theconnection point of switches SbP and SbN). In the half bridgeconfiguration 895, an output AC voltage may be taken from intermediatenodes a (located at the connection point of switches SaP and SaN) and b(located at the connection point of input capacitors C1 and C2).

For operation as an AC-AC converter, each topology 894-895 may beoperated using pulse width modulation to generate the desired outputvoltage for convenience outlet 804. Such PWM modes of operation arebroadly similar to those discussed above, accounting for thebidirectionality of the switching devices. These PWM modes of operationare applicable to all of the operating modes described above withreference to FIGS. 4-7 in which converter 407 provides AC voltageregulation for convenience outlet 404/804. Alternatively, convertertopologies may also operate in a pass-through mode, in which the inputvoltage appearing across terminals P/Q is passed directly to outputterminals a/b. This passthrough mode of operation is applicable to allof the operating modes described above with reference to FIGS. 4-7 inwhich converter 407 does not provide AC voltage regulation forconvenience outlet 404/804. Additionally, converter topologies 894-895can include output filter and zero voltage switching circuits asdescribed above with respect to FIG. 8 .

The foregoing describes exemplary embodiments of battery-based DC powersystems that may repurpose charger circuitry to provide an AC voltagefor convenience outlets or other AC loads. Such systems may be used in avariety of applications but may be particularly advantageous when inconjunction with electric and hybrid electric vehicles, grid batterystorage systems, portable power banks, and the like. Although numerousspecific features and various embodiments have been described, it is tobe understood that, unless otherwise noted as being mutually exclusive,the various features and embodiments may be combined in variouspermutations in a particular implementation. Thus, the variousembodiments described above are provided by way of illustration only andshould not be constructed to limit the scope of the disclosure. Variousmodifications and changes can be made to the principles and embodimentsherein without departing from the scope of the disclosure and withoutdeparting from the scope of the claims.

Additionally, it is well understood that the use of personallyidentifiable information should follow privacy policies and practicesthat are generally recognized as meeting or exceeding industry orgovernmental requirements for maintaining the privacy of users. Inparticular, personally identifiable information data should be managedand handled so as to minimize risks of unintentional or unauthorizedaccess or use, and the nature of authorized use should be clearlyindicated to users.

1. An AC-AC converter comprising: a stack of four switching devices,wherein an input of the AC-AC converter is coupled across the stack offour switching devices and an output of the AC-AC converter is takenfrom first terminal coupled to a connection point of first and secondswitching devices of the stack and a second terminal coupled to aconnection point of third and fourth switching devices of the stack;first and second series-connected input capacitors coupled across theinput of the AC-AC converter, with a connection point of theseries-connected input capacitors coupled to a connection point of thesecond and third switching devices; and at least one output filterinductor and at least one output filter capacitor coupled to the outputof the AC-AC converter.
 2. The AC-AC converter of claim 1 wherein the atleast one filter inductor comprises a first filter inductor coupledbetween the first terminal and a load.
 3. The AC-AC converter of claim 2wherein the at least one filter inductor comprises a second inductorcoupled between the second terminal and the load.
 4. The AC-AC converterof claim 1 further comprising a resonant tank made up of at least oneresonant capacitor and at least one resonant inductor, wherein theresonant tank facilitates zero voltage switching of the switchingdevices.
 5. The AC-AC converter of claim 4 wherein the resonant tank isa series resonant circuit coupled between the first terminal and thesecond terminal.
 6. The AC-AC converter of claim 4 wherein the resonanttank is a series resonant circuit coupled in parallel with the at leastone output filter inductor.
 7. An AC-AC converter comprising: a stack offour switching devices, wherein an input of the AC-AC converter iscoupled across the stack of four switching devices and an output of theAC-AC converter is taken from first terminal coupled to a connectionpoint of first and second switching devices of the stack and a secondterminal coupled to a connection point of third and fourth switchingdevices of the stack; and a controller that operates the switchingdevices such that: during a positive half cycle of an AC input voltage,first and second switching devices of the stack are operated with analternating 50% duty cycle and third and fourth switching devices of thestack are constantly on; and during the negative half cycle of the ACinput voltage, the third and fourth switching devices of the stack areoperated with an alternating 50% duty cycle and the first and secondswitching devices of the stack are constantly on.
 8. The AC-AC converterof claim 7 wherein: during the positive half cycle, the duration of theon-times of the first and second switching devices determine themagnitude of the AC voltage between the first and second terminals; andduring the negative half cycle, the duration of the on times of thethird and fourth switching devices determine the magnitude of the ACvoltage between the first and second terminals.
 9. The AC-AC converterof claim 7 further comprising first and second series-connected inputcapacitors coupled across the input of the AC-AC converter, with aconnection point of the series-connected input capacitors coupled to aconnection point of the second and third switching devices.
 10. TheAC-AC converter of claim 7 further comprising at least one output filterinductor and at least one output filter capacitor coupled to the outputof the AC-AC converter.
 11. The AC-AC converter of claim 10 wherein theat least one filter inductor comprises a first filter inductor coupledbetween the first terminal and a load.
 12. The AC-AC converter of claim11 wherein the at least one filter inductor comprises a second inductorcoupled between the second terminal and the load.
 13. The AC-ACconverter of claim 7 further comprising a resonant tank made up of atleast one resonant capacitor and at least one resonant inductor, whereinthe resonant tank facilitates zero voltage switching of the switchingdevices.
 14. The AC-AC converter of claim 13 wherein the resonant tankis a series resonant circuit coupled between the first terminal and thesecond terminal.
 15. The AC-AC converter of claim 13 wherein theresonant tank is a series resonant circuit coupled in parallel with theat least one output filter inductor.
 16. A method performed by acontroller of an AC-AC converter having a stack of four switchingdevices, wherein an input of the AC-AC converter is coupled across thestack of four switching devices and an output of the AC-AC converter istaken from first terminal coupled to a connection point of first andsecond switching devices of the stack and a second terminal coupled to aconnection point of third and fourth switching devices of the stack, themethod comprising: during a positive half cycle of an AC input voltage:operating first and second switching devices of the stack with analternating 50% duty cycle; and turning on and leaving on third andfourth switching devices of the stack; and during a negative half cycleof the AC input voltage: operating the third and fourth switchingdevices of the stack with an alternating 50% duty cycle; and turning onand leaving on the first and second switching devices of the stack. 17.The method of claim 16 wherein: during the positive half cycle, theduration of the on-times of the first and second switching devicesdetermine the magnitude of the AC voltage between the first and secondterminals; and during the negative half cycle, the duration of the ontimes of the third and fourth switching devices determine the magnitudeof the AC voltage between the first and second terminals.
 18. The methodof claim 16 wherein the switching devices are operated with zero voltageswitching.
 19. An AC-AC converter comprising: a plurality ofbidirectional switching devices, wherein an input of the AC-AC converteris coupled across the bidirectional switching devices, and an output ofthe AC-AC converter is taken from a connection point of thebidirectional switching devices; at least one input capacitor coupledacross the input of the AC-AC converter; and at least one output filterinductor and at least one output filter capacitor coupled to the outputof the AC-AC converter.
 20. The AC-AC converter of claim 19 wherein thebidirectional switches are configured as a full bridge converter. 21.The AC-AC converter of claim 19 wherein the bidirectional switches areconfigured as a half bridge converter.
 22. The AC-AC converter of claim19 wherein the at least one filter inductor comprises a first filterinductor coupled between the first terminal and a load.
 23. The AC-ACconverter of claim 22 wherein the at least one filter inductor comprisesa second inductor coupled between the second terminal and the load. 24.The AC-AC converter of claim 19 further comprising a resonant tank madeup of at least one resonant capacitor and at least one resonantinductor, wherein the resonant tank facilitates zero voltage switchingof the switching devices.